United States Patent 5,279,811: Scope of Claims and US Landscape
US Patent 5,279,811 claims a family of lipophilic, charge-neutral radiopharmaceuticals formed by complexing a radionuclide with a diamine-dithiol (diaminodithiol) ligand that is structurally defined by a variable substituent system (formulas A and B). The claims extend to brain radioimaging via parenteral administration and subsequent imaging after localization.
What is the protected invention?
Core claim concept (product)
The foundational claim (claim 1) is directed to:
- Radiopharmaceutical
- Lipophilic, charge neutral complex of:
- a radionuclide and
- a diaminodithiol ligand
- where the diaminodithiol is selected from structurally defined ligands (formula A or B), including ester-functional substituents on the ligand, and
- where at least one of R1 to R12 is --A--COOR
- and where the product is in sterile, pharmaceutically acceptable form, including pharmaceutically suitable salts.
This establishes a claim architecture with three adjustable axes:
- Radionuclide identity (claim 2 and onward)
- Ligand scaffold identity and substituent pattern (claims 1 and 4)
- Pharmaceutical form and brain-imaging use (claims 18-34)
Core use concept (method)
Claims 18-34 claim a method of radioimaging the brain comprising:
- Parenteral administration to a mammal of an effective amount of the claimed radiopharmaceutical (depending on the specific composition claim incorporated), in a pharmaceutically suitable carrier, and
- Radioimaging the brain after sufficient time for the composition to localize in the brain.
The “radioimaging” method claims largely differ only by which composition claim they incorporate.
What do the key composition claims actually cover?
Claim 1: Broadest product scope
Claim 1 covers radiopharmaceuticals that meet all conditions below:
A. Complex character
- The complex is lipophilic and charge neutral.
- It is formed between a radionuclide and a diaminodithiol ligand.
B. Ligand family selection
- The diamino-dithiol is selected from formula A or formula B (not reproduced in full text here, but referenced as ##STR12##).
C. Substituent system
Each of R1-R12 is independently selected from:
- H
- alkyl (C1-C10)
- --A--COOR, where:
- A is a straight or branched alkylene (C0-C10)
- n, o, p are independently 1 or 2
- R is selected from:
- alkyl (C1-C10)
- phenyl or benzyl with up to 5 ring substituents chosen from:
- alkyl (C1-C4), fluoro, chloro, bromo, nitro,
- alkoxy (C1-C4),
- carboxyl or carboxylic acid ester (C1-C4)
- a 5- or 6-membered heterocycle with 1 or 2 heteroatoms from N, O or X
D. Ester requirement
- At least one of R1-R12 must be --A--COOR.
- This “at least one esterified substituent” requirement narrows the family to ester-functional members within formulas A/B.
E. Formulation requirement
- Sterile, pharmaceutically acceptable form.
- Includes pharmaceutically suitable salts.
Practical effect: claim 1 is a “belt-and-suspenders” claim: broad on radionuclides later, broad on substituent chemistry, but pinned to:
- the diamino-dithiol structural family (A/B),
- the presence of at least one ester-substituent group, and
- lipophilic/charge-neutral complex behavior.
Claim 2-3: Radionuclide range then technetium-99m
Claim 2 expands radionuclide scope to:
- Tc, Ru, Cu, Co, Pt, Fe, Os, Ir, W, Re, Cr, Mo, Mn, Ni, Rh, Pd, Nb, Ta (radioactive isotopes)
Claim 3 narrows to:
Practical effect: claim 3 is a focused subset within claim 2, which itself is a wide list. If a candidate radiopharmaceutical uses any radionuclide outside that list, it is outside these dependent claim scopes, though claim 1 alone does not explicitly list radionuclides in the text provided. In the claim set you supplied, the radionuclide universe is expressly set by claim 2/3/5/6, so these dependent claims drive enforceable radionuclide boundaries.
Claim 4-6: A narrower diamino-dithiol formula and Tc-99m subgroup
Claim 4 defines the diamino-dithiol with a specific formula reference ##STR13## and changes the substituent limits:
Each R1-R12 is independently selected from:
- H
- alkyl (C1-C6)
- --A--COOR
- A is alkylene (C0-C6)
- n,o,p are independently 1 or 2
- R is alkyl (C1-C6) (no phenyl/heterocycle expansion in claim 4’s R definition)
Ester requirement: at least one of R1-R12 is --A--COOR.
Claim 5 repeats the radionuclide list from claim 2 (same set).
Claim 6 narrows to technetium-99m.
Practical effect: claim 4 is a “reduced substituent diversity” version of claim 1, limiting the allowed ester-bearing substituent chemistry more tightly (alkyl-only for R in the ester case; no aryl/heterocycle options in the parameter set shown).
Claims 7-14: Parameter tightening (carbon counts, A length, stereochemistry)
These dependent claims carve out subranges inside the claim 6/4 framework:
Claim 7
- Tc-99m radiopharmaceutical
- R and any alkyl in R1-R12 is C1-C3
Claim 8
- A is straight chain alkylene C0-C3
Claim 9
- n=o=p=1
- and R3 and R10 contain --A--COOR (as presented: “and R1-4 of R1-R12 is --A--COOR,” with numbering text inconsistently rendered; the intent is an ester presence constraint at specific positions)
Claim 10
- diamino-dithiol is “non-aminated”
- R and alkyl in R1-R12 is C1-C3
Claim 11
- Tc-99m
- R3 and R10 are --A--COOR
- R4 and R9 are H
- n=o=p=1
Claim 12
- Tc-99m
- A is a bond
- R is ethyl
Claim 13
- Tc-99m
- A is a bond
- stereochemistry at the backbone attachment position is L
Claim 14
- Tc-99m
- n=o=p=1
- R3 and R10 are --A--COOR where:
- A is straight chain alkylene C0-C3
- R is alkyl C1-C3
- R4 and R9 are H
- R1,R2,R5,R6,R7,R8,R11,R12 are each H or alkyl C1-C3
Practical effect: claims 7-14 define a relatively specific subfamily, including explicit constraints on:
- carbon counts,
- which positions carry ester groups,
- “A is a bond” and “A is short alkylene,” and
- L stereochemistry.
These claims are the most operationally constraining for designing around: a competitor can aim to change any of these structural constraints and move out of these dependent claim scopes, but claim 1/4 remain broader targets unless the ligand architecture is changed beyond A/B formulas.
Claims 15-17: Specific named ligands
These claims anchor the family to concrete ligands:
Claim 15
- diamino-dithiol: N,N'-1.2-ethylenedi-ylbis-L-cysteine, diethyl ester
Claim 16
- N,N'-1.2-ethylene-diylbis-L-cysteine, dimethylester, dihydrochloride
Claim 17
- N,N'-1,2-ethylene-diylbis-L-cysteine, di-n-polyester, dihydrochloride (as rendered)
Practical effect: these are “spot claims” that can be asserted even if the broader variable-parameter claims are contested on interpretation. If any competitor uses these exact named ligands (or salts described), it is directly inside at least these dependent scopes (subject to the composition also being a lipophilic, charge-neutral complex with the claimed radionuclide and ligand structure family).
What is the method scope for brain imaging?
Claims 18-34: Parenteral administration plus brain localization time
All method claims follow the same template:
- Administer parenterally to a mammal
- an effective amount of the radiopharmaceutical of the incorporated composition claim
- in a pharmaceutically suitable carrier
- then radioimage the brain after sufficient time for localization
The only differences are which composition claim is incorporated:
- claims 18-20 follow 1-3,
- claims 21-23 follow 4-6,
- claims 24-26 follow 7-9,
- claims 27 repeats claim 6,
- claims 28-34 correspond to specific later composition claims (11-14, 15, 11 again, and 12-13 in sequence as rendered).
Practical effect: the method claims do not appear to define imaging modalities (PET, SPECT) or specific time windows. Enforceability typically depends on interpretation of “sufficient time for localization” and whether accused products are administered parenterally with brain imaging as claimed.
Claim-by-claim scope map (what you can build inside vs outside)
| Segment |
Claim range |
What changes within scope |
Hard constraint visible in text |
| Ligand family |
1 |
R1-R12 ∈ {H, alkyl C1-C10, --A--COOR (A C0-C10, R wide: alkyl/aryl/heterocycle)} |
“at least one R1-R12 is --A--COOR” + ligand is formula A or B |
| Ligand family narrower |
4 |
R and A reduced to alkyl-only for ester R; A C0-C6; alkyl C1-C6 |
“at least one R1-R12 is --A--COOR” + ligand is formula in ##STR13## |
| Radionuclide universe |
2,5 |
Tc plus broad set of transition metals |
must be in listed set in dependent claims |
| Tc-99m subset |
3,6-7,8,9-14,15-17 |
fixation to 99mTc |
radionuclide must be 99mTc |
| Position and stereochemical constraints |
7-14 |
carbon-count tightening; A length; n,o,p; specific ester positions; L stereochemistry |
explicit position constraints like R3/R10 ester; R4/R9 H; “A is bond” |
| Concrete ligands |
15-17 |
specific cysteine-based diaminodithiol esters/salts |
exact ligand identity/salt |
| Use scope |
18-34 |
which composition claim is used |
parenteral administration + brain imaging after localization |
Patent landscape: what is likely to be the competitive battleground in the US
1) Composition space is the main contested area
Given the structure-first nature of claims 1 and 4 (ligand formulas A/B and ##STR13##), a US infringement fight will turn on:
- whether the accused ligand matches the claimed diamino-dithiol structural definitions,
- whether it has the required ester-substitution rule (“at least one R1-R12 is --A--COOR”), and
- whether the complex is “lipophilic” and “charge neutral” as characterized in the patent.
If a competitor alters the ligand backbone away from the claimed diamino-dithiol formulas, it can move outside even if the imaging workflow matches claims 18-34.
2) Tc-99m targeting is a major value driver
Claims 3 and 6 plus the dependent chain (7-14, 15-17) indicate a focus on 99mTc brain imaging radiopharmaceuticals. Competitors in this area typically face two options:
- keep the ligand family close and try to design around the narrower sub-parameter constraints (carbon counts, ester position, stereochemistry), or
- change the ligand scaffold so that the product is no longer within the defined diamino-dithiol formulas.
3) “Spot” ligands narrow design-around options
Claims 15-17 explicitly name particular diaminodithiol esters and salts derived from L-cysteine units with an ethylene-diyl backbone. If a competitor’s ligand is essentially the same (or a salt-equivalent that meets “pharmaceutically suitable salts”), it becomes harder to avoid these dependent claims.
4) Method claims rely on “parenteral” administration and brain localization
The method claims are broad and operational, but they are also easier to avoid by:
- using a different route than “parenterally,” or
- targeting a different organ or imaging target, or
- using a different radiopharmaceutical that does not fall inside the composition claims.
However, if the product is within the composition claims, the method claims can create an additional infringement vector tied to standard clinical workflows.
Key takeaways
- US 5,279,811 protects a ligand-defined, lipophilic, charge-neutral radiopharmaceutical complex where the ligand is a diaminodithiol in formula A/B (or the specific formula in claim 4).
- The composition claims are anchored by a non-optional chemical rule: at least one ester substituent (--A--COOR) on R1-R12.
- Tc-99m is a central subset (claims 3,6 and dependent claims 7-14 and 15-17).
- The narrow dependent claims (7-14) constrain carbon counts, which substituents are esterified, A definition (including “A is a bond”), and L stereochemistry.
- The use claims (18-34) are parenteral administration + brain imaging after localization, with breadth driven by the incorporated composition claim rather than imaging protocol details.
FAQs
1) What is the single most important chemical limitation in claim 1?
At least one of R1-R12 must be --A--COOR (ester substitution), while the ligand must match formula A or B and form a lipophilic, charge-neutral complex.
2) Does the patent protect only technetium-99m radiopharmaceuticals?
No. Claim 2 covers a listed set of radionuclides; claim 3 and downstream dependents narrow to technetium-99m.
3) How do claims 4 and 1 differ in practical design terms?
Claim 4 narrows the substituent system by limiting ester substituent R and A to shorter alkyl-only definitions, while maintaining the ester-required rule and restricting the diamino-dithiol to the specific formula shown as ##STR13##.
4) Which dependent claims are most likely to matter for strict design-around?
Claims 7-14 because they add explicit restrictions on carbon number, which positions bear esters, A being bond/short alkylene, and L stereochemistry, on top of the underlying formula constraints.
5) What does the method claim add beyond the composition?
It adds a workflow limitation: parenteral administration followed by brain radioimaging after localization. If a radiopharmaceutical is outside the composition claims, the method claims typically do not apply.
References
[1] United States Patent No. 5,279,811.
